Tank-type vacuum cleaners are capable of receiving dry materials such as debris or dirt and may also be used for suctioning liquids. When the tank is full, an upper vacuum assembly (which often includes a motor and an air impeller) is removed and the contents are dumped out. If the vacuum cleaner is used on liquid material, the tank, when at or near capacity, may be very heavy so that lifting the tank, to pour the contents into a sink or the like, is difficult. Even tilting the tank to pour the contents into a floor drain may be unwieldy when the liquid level in the tank is high.
One solution to the difficulties encountered in emptying liquid from vacuum tanks has been to provide an outlet at the bottom of the tank. Such a solution is satisfactory when the contents of the tank are emptied into a floor drain; however, if no floor or other low-placed drain is available the tank must be lifted to a sink or similar disposal site. In such cases the outlet at the bottom of the tank is of little value.
A second solution to emptying a vacuum tank of liquid is to provide a pump, usually with a motor located outside of or in the bottom of the tank. The pump removes liquid through a lower portion of the tank and expels it through a hose to waste. While such pumps are generally effective, they may be very costly. The pump requires not only a pump impeller and hoses but also its own electric motor, power cords, and switches. The expense of such items may be significant in the context of the overall cost of a vacuum cleaner, particularly those designed for residential use. Such pumps may also reduce the effective capacity of the vacuum tank or interfere with operation when the vacuum cleaner is used on dry materials. In addition, it may also be necessary to provide costly or complicated structures to prime the pump, if it is not located in the bottom of the tank.